Newtown shooting: Final report reveals 'painful' details

US police have released thousands of documents related to their investigation into the killing of 26 people at a school in Connecticut.

Officials described as "painful" some of the details in the report, which includes photos and transcripts.

It reveals new facts about the life of gunman Adam Lanza, 20, said to have suffered from mental health issues.

Lanza turned a gun on himself after opening fire at Sandy Hook Elementary School in Newtown in December 2012.

Before killing 20 children and six adults with a semi-automatic rifle, he shot dead his own mother at the family home. She had bought him the weapons used in the rampage.

Adam Lanza killed his mother at home before driving to the school

Last month, Connecticut police published a summary of their findings, showing that Lanza had "an obsession" with the 1999 Columbine massacre, during which two teenagers killed 12 students and a teacher.

Investigators also found that Lanza had acted alone and planned the shooting, which took less than 11 minutes.

'Destruction and war'

The final report contains evidence that Lanza's mother discussed her son's "disabilities" with a friend the day before the Sandy Hook attack.

One of the gunman's former teachers said Lanza's creative writing was "so graphic that it could not be shared". The student would "write 10 pages obsessing over battles, destruction and war".

The findings also reveal autopsy reports and new information about how the shooting unfolded.

A teacher hiding in a closet said he heard janitor Rick Thorne challenge Lanza. Mr Thorne, who survived the attack, apparently yelled "Put the gun down".

Among the audiovisual material released on Friday were photos of items found in Lanza's home, including numerous rounds of ammunition, gun magazines, shooting earplugs and a gun safe with a rifle in it.

The files were heavily redacted to protect the students' identity and to withhold gruesome details of the crime.

The Newtown shooting prompted a renewed US campaign for stricter firearms controls.

While no legislation was passed at a national level, some states - including Connecticut and Colorado - imposed tougher gun laws. Other states loosened restrictions.

The report includes photos of bullets and a gun magazine

An assault-style rifle was found inside Sandy Hook Elementary School after the shooting

Several swords, a bayonet and more than 1,000 rounds of ammunition were found at Lanza's home